Many houses and other buildings use warm air furnaces to provide heat. Generally, these furnaces operate by heating air received through cold air or return ducts and distributing the heated air throughout the building using warm air or supply ducts. A circulation fan, operated by an alternating current (AC) permanent-split-capacitor (PSC) motor, directs the cold air into a heat exchanger, which may be composed of metal. The heat exchanger metal is heated using a burner that burns fossil fuels. The burner is ignited with an ignition device, such as an AC hot surface ignition element. The air is heated as it passes by the hot metal surfaces of the heat exchanger. After the air is heated in the heat exchanger, the fan moves the heated air through the warm air ducts. A combustion air blower, or inducer, is used to remove exhaust gases from the building. The inducer is typically operated using an AC shaded-pole motor.
Because furnaces play a critical role in the comfort of the occupants of the building, it is important that the warm air furnace remains functional. Therefore, it is desirable to detect faults in the warm air furnace prior to failure. This may prevent the occupants of the building from either remaining in an uncomfortably cold building or having to leave the building while waiting for a repair technician to fix the warm air furnace.
Therefore, a need exists to detect faults in a warm air furnace while the furnace is operating. Detecting faults in a warm air furnace while the furnace is operating may be beneficial for allowing an installer to verify proper furnace operation prior to leaving a site of installation, enabling predictive diagnostics for detecting deteriorating furnace elements prior to failure, and quickly detecting faults that have already occurred.